1. Field of the Invention
The invention relates to heat integration of a catalytic hydrogenation process. More particularly the invention relates to preheating a portion of feedstock by indirect heat exchange with hot reactor effluent. Most particularly the invention relates to quenching the entire hot reactor effluent with a predetermined amount of feedstock.
2. Description of Other Related Methods in the Field
Hydrotreaters are employed in petroleum refineries to hydrogenate petroleum derived stocks. Hydrogenation removes sulfur, nitrogen, metals and other undesirable contaminants from the stock. Hydrogeneration also saturates olefinic and aromatic compounds rendering the stock more stable to thermal degradation as well as stabilizing color.
Hydrotreating is typically carried out in a packed bed of catalyst. Hydrotreating catalysts typically comprise a Group IV metal or a Group VI metal on a porous solid support. The most typical metals are nickel, Raney nickel, cobalt and molybdenum. Cobalt-molybdenum and nickel-molybdenum on an aluminum support are in wide commercial use in the industry for this purpose. The hydrogeneration reaction is carried out at a hydrogen partial pressure of 100 to 2000 psia and a temperature of 400.degree. F. to 800.degree. F.
A hydrotreater typically comprises a charge pump, a make-up hydrogen compressor, feed/effluent and hydrogen/effluent heat exchangers, a charge heater, one or more reactors, product separators, a recycle hydrogen compressor and product fractionators.
The feed/effluent and hydrogen/effluent exchangers are used to preheat the reactants. The charge heater supplies the remaining heat to bring the feed to reactor inlet temperature. The reactor effluent is cooled several hundred degrees before reaching the product separators. Heat is recovered by heat exchange with the reactants. Hydrogen and oil may be mixed either upstream or downstream of the feed/effluent exchangers. Mixing upstream of the exchangers provides greater temperature differentials, higher heat transfer coefficients and reduced fouling. This is typical of a feed which is fully vaporized in the exchangers. However, when a mixed phase is fed to the reactors and/or charge heaters this can be a problem except for small units with a single pass heater (less than 5000 barrels per day). In all but the small units the mixed hydrogen and oil must be fed to a multi-pass heater. To avoid maldistribution in the multiple passes there must be a flow control valve on each pass. Since two-phase mixtures are hard to measure and control the hydrogen and oil must be passed through separate heat exchangers trains.